1. Field of the Invention
One or more exemplary embodiments relates to a magnetic jack type in-vessel control element drive mechanism, and more particularly, to a magnetic jack type in-vessel control element drive mechanism which makes a control element assembly move up and down through magnetic force, minimize the loss of magnetic force, simplify the assembly process and be operable under high-temperature, high-pressure and high-radiation conditions.
The present invention is derived from research conducted as part of the Nuclear Power Core Technology Development Program by the Ministry of Trade, Industry & Energy [Project Serial Number: 20131510101680, Title of Research Project: Development of Top-Mounted ICI System and In-Vessel Control Element Drive Mechanism for Severe Accident Mitigation Design.
2. Description of the Related Art
A control element drive mechanism is provided to control the power of a nuclear reactor and is classified as, for example, a magnetic-jack type control element drive mechanism, a ball-screw type control element drive mechanism, and a hydraulic type control element drive mechanism. The present invention relates to a magnetic jack type control element drive mechanism.
FIG. 1 is a conceptual installation view of a conventional control element drive mechanism, and FIG. 2 is a schematic cross-sectional view of the conventional control element drive mechanism.
As shown in FIG. 1, a nuclear fuel assembly 2 and a control element 3 are placed in a nuclear reactor 1. The control element 3 controls the fission of the nuclear fuel by adjusting the number of neutrons absorbed by a nuclear fuel. The control element 3 is vertically driven up and down by the control element drive mechanism 5. For the installation of the control element drive mechanism 5, a nozzle 4 is placed on a top portion of the nuclear reactor 1.
The control element drive mechanism 5 includes four coils, i.e., an upper lifting (UL) coil 510, an upper gripper (UG) coil 520, a lower lifting (LL) coil 530, and a lower gripper (LG) coil 540, and controls the vertical movement of the control element 3 by controlling magnetic force generated by the coils.
However, the conventional control element drive mechanism has a drawback of requiring a cooling system which provides cooling air to remove the heat of the coils during operation.
Moreover, a motor assembly is located inside a motor housing 560, and at the center of the motor assembly, a drive shaft 6 connected to the control element 3 is placed. The considerable amount of magnetic flux generated by the above-mentioned driving coils is not transferred to the motor assembly but bypasses through the motor housing 560, thereby causing a reduction in magnetic force. To compensate for such reduction in magnetic force, grooves 561 are formed on an outer circumferential surface of the motor housing 560. However, the grooves 561 may not compensate enough for the loss of magnetic force.
Also, small nuclear reactors, which have drawn much attention recently, often require control element drive mechanisms installed inside the nuclear reactor according to system requirements. Under these circumstances, usability of the control element drive mechanism under the conditions of much higher temperature, pressure and radiation is more required than in conventional nuclear reactors. Therefore, there is a demand for a new control element drive mechanism which is different from conventional control element drive mechanisms.